1. Field of the Invention
The present invention relates generally to radiation-receiving devices, and more particularly, to a self-calibrating radiometer.
2. Description of the Prior Art
A radiometer is an instrument for measuring radiated flux and is typically used to measure light output from an object, temperature of foundry melts, temperature of stars, etc. A conventional radiometer includes an optical system for collecting energy from a source under examination and for focusing the energy, a temperature-sensing element such as a temperature sensitive resistor or bolometer, for receiving the focused energy and providing an electrical output of its temperature, and an electrical measuring system for providing an indication of the source temperature in response to the electrical output.
Heretofore, one of the disadvantages of such radiometers was that each was required to be calibrated against a "standard" radiating body of known temperature and known surface emissivity. The problem associated with calibrating a radiometer is that of duplicating in the radiometer an equivalent radiation temperature of a high temperature or a distant object. Because of this problem the prior art devices have been unsatisfactory in measuring high-temperature, distant objects, such as stars, etc.
In the prior art radiant energy measuring systems which are disadvantageous in that they require calibration are found in the U.S. Pat. Nos. 2,305,396, Volochine, and 3,566,122, Paine.
Other instruments that are used to measure fundamental properties of heat-producing objects include radiation pyrometers which are used to measure the temperature of the object.
An example of a pyrometer, or temperature-measuring instrument is found in U.S. Pat. No. 3,164,021, DeJong et al. The DeJong device includes a radiation receiver having front and back surfaces and a heating element embedded therein for equalizing the temperature on the front and back surfaces. A differential thermocouple is associated with the radiation receiver and serves to measure the temperature difference between the front and back surface, and a measuring thermocouple is disposed within the windings of the differential thermocouple and serves to measure the absolute temperature of the front surface. In operation, the heating element supplies energy to the device to equalize the temperatures of the front and back surfaces, thereby permitting the temperature of the front surface to be measured. However, this device is disadvantageous in that it must be calibrated and is limited to measuring the temperature of objects whose equivalent radiation temperature can be conveniently duplicated in the measuring instrument.